mirror of https://github.com/vitalif/e2fsprogs
libext2fs: fix Direct I/O fallback code so it implements RMW correctly
There is a bug in Unix I/O manager where if an aligned I/O is required, it does not correctly do the read-modify-write cycle correctly. Specifically, it was not doing an lseek between the read and the write calls, so the update was going to block N+1 instead of block N. Oops. Fortunately in practice we almost never use this fallback path, so file systems weren't getting horribly corrupted, because (a) we almost never use Direct I/O in e2fsprogs, at least not by default, and (b) when we do the buffers end up being aligned anyway, so it's OK. We only noticed this because the new Undo I/O manager in e2fsprogs 1.43 was doing unaligned I/O and FreeBSD requires that I/O requests be aligned even if you are not doing Direct I/O, and the e2undo regression tests were all failing as a result. Signed-off-by: Theodore Ts'o <tytso@mit.edu>maint
parent
be5ce27525
commit
127e2291bf
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@ -282,6 +282,10 @@ static errcode_t raw_write_blk(io_channel channel,
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if (size > channel->block_size)
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actual = channel->block_size;
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memcpy(data->bounce, buf, actual);
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if (ext2fs_llseek(data->dev, location, SEEK_SET) != location) {
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retval = errno ? errno : EXT2_ET_LLSEEK_FAILED;
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goto error_out;
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}
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actual = write(data->dev, data->bounce, channel->block_size);
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if (actual != channel->block_size)
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goto short_write;
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